The object of this invention is to provide a new, economical process for the selective production at high yield of 3-methylpyridine (also called beta-picoline) through the catalytic cyclization of a pentanediamine derivative, namely 2-methyl-1,5-pentanediamine. Another object is the similar conversion of a mixture of this acyclic compound and a piperidine derivative, namely 3-methylpiperidine (also called beta-pipecoline), to the same desired 3-methylpyridine product.
As background, the value of this invention is enhanced by the fact that the starting materials are readily available often as by-products from the manufacture of other large-volume products. For instance, in the manufacture of adiponitrile which is an important intermediate in making nylon, the addition of hydrogen cyanide to butadiene also gives 2-methylglutaronitrile (MGN) as a by-product in large quantities. Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Vol. 15, p. 899; U.S. Pat. Nos. 3,542,847 and 3,551,474. Hydrogenation of this MGN can then provide 2-methyl-1,5-pentanediamine (MPDA) as a major product.
For example, British Patent No. 1,488,335 issued in 1977 to Dynamit Nobel describes MGN hydrogenation in the prior art to mostly 2-methyl-1,5-pentanediamine (MPDA) and some 3-methylpiperidine, while examples in the '335 patent describe reversed product ratios as its invention. U.S. Pat. No. 2,790,804 issued in 1957 to ICI and British Patent No. 2,165,844 issued in 1986 to ICI similarly describe hydrogenation of unsubstituted glutaronitrile to pentanediamine and piperidine. MPDA can also be conveniently prepared by hydrogenation of 2-methyleneglutaronitrile, which is a product of the dimerization of acrylonitrile. British Patent No. 1,164,354 issued in 1969 to Toyo Rayon; U.S. Pat. No. 3,225,083 issued in 1965 to Shell; U.S. Pat. No. 3,562,311 issued in 1971 to Shell; and U.S. Pat. No. 4,422,981 issued in 1983 to Mitsubishi.
Pyridine derivatives, on the other hand, are known to be useful for many purposes. For example, pyridine is valuable as a solvent and as an intermediate for agricultural chemicals. 3-Methylpyridine (beta-picoline) is itself useful as a solvent and as an intermediate for the manufacture of nicotinic acid and nicotinamide, both forms of the pellagra-preventative vitamin. Goe, "Pyridine and Pyridine Derivatives", Kirk-Othmer, Encyclopedia of Chemical Technology, Third Edition, Vol. 19.
In the past, cyclization and dehydrogenation reactions known to produce pyridine and its derivatives have been comprehensively reviewed originally by Brody and Ruby in Volume 1 of Pyridine and Its Derivatives, E. Klingsberg, ed., and most recently by Bailey, Goe and Scriven, in Vol. 5 of the Supplement to Pyridine and Its Derivatives, G. C. Newkome, ed. These reactions have generally been carried out in the gas phase at low to moderate temperatures up to about 400.degree. C. and for various times using predominantly precious metal catalysts such as palladium and platinum. For example, British Patent No. 755,534 issued in 1956 to ICI describes the conversion of pentanediamine (PDA) to pyridine in 55% yield using a catalyst of 5% platinum on a silica support at 400.degree. C. This document also reports the conversion of PDA to piperidine using acidic heterogeneous catalysts such as silica, silica-alumina beads and boron phosphate, without the precious metal or any other metal component at 350.degree. C. Other examples include the following:
Netherlands patent application No. 7,005,792 (Deumens, Groen, and Lipsch, 1971 to Stamicarbon; Chem. Abstr., 76, 46099) reports converting PDA to piperidine in high yield using a catalyst of Raney-nickel supported on silica or to various mixtures of piperidine and pyridine using a catalyst of palladium supported on alumina at 125.degree.-300.degree. C.
U.S. Pat. No. 4,086,237 issued in 1978 to Dynamit Nobel (equivalent to German Patent No. 2,519,529) reports the conversion of MPDA alone or with 3-methylpiperidine to mostly 3-methylpyridine using palladium metal on an alumina support at 200.degree.-400.degree. C. U.S. Pat. No. 4,401,819 issued in 1983 to Rhone-Poulenc reports a similar conversion using a precious metal on a particular macroporous solid silica support at 200.degree.-500.degree. C. However, no examples are given at the upper end of this temperature range, and preferred temperatures are reported to be 250.degree.-400.degree. C.
British patent application No. 2,165,844 filed in 1986 by ICI reports the eventual conversion of glutaronitrile to pyridine, perhaps with the preferred isolation of 1,5-pentanediamine as an intermediate, using palladium metal on silica support at 350.degree.-400.degree. C.
Collectively, these references show that pentanediamine and its alkyl derivatives have been selectively converted in the past to their piperidine counterparts using catalyst supports alone or in combination with the Group VIII nickel metal, or to admixtures of these piperidines and their pyridine counterparts using various Group VIII precious metals (also called noble metals) including palladium and platinum at moderate temperatures of about 400.degree. C. This work has suffered from the disadvantage that only these precious metal catalysts have been shown to selectively produce acceptably-high yields of the pyridine compounds such as 3-methylpyridine. Besides their high initial cost, these expensive precious metal catalysts pose added handling problems and cannot be economically used in fluid-bed reactors (which are advantageous for many reasons including their temperature uniformity and ease of catalyst regeneration) because of the catalyst losses that inevitably occur in such processes.
Thus, there has been a growing need and economic driving force for a process useful for the selective conversion of pentanediamine derivatives (such as 2-methyl-1,5-pentanediamine) to their pyridine counterparts (such as 3-methylpyridine) in high yields using effective and readily available catalysts that are inexpensive, that are susceptible of regeneration, and that most preferably can be operated in fluid-bed reactors. The applicants' pending U.S. patent application Ser. No. 217,686, filed Jul. 11, 1988 and entitled PROCESS FOR SELECTIVE PRODUCTION OF 3-METHYLPYRIDINE describes additional work by the applicants to date to meet these needs. In particular, this prior application describes a process for the selective production of 3-methylpyridine in high yield using preferred transition metal-oxide catalysts of copper chromium or molybdenum. These preferred catalysts are inexpensive as compared to the Group VIII precious metal catalysts of the prior art while performing comparably thereto at temperatures predominantly used in the prior art, namely, about 400.degree. C.
Nevertheless, there remains a need for a process for the selective production of 3-methylpyridine which is not critically limited to select few, and often expensive catalysts as in the case of precious metals. The applicants, through their continued work in this field, have made a surprising and significant discovery which meets this need.